The invention relates to polymeric materials and particularly, although not exclusively, relates to polymeric materials for use in applications wherein the material is subject to high temperature, high pressure and corrosive chemicals, for example in oil and/or gas installations.
One of the most challenging environments in which a material may be used is underground in oil and gas production. In oil and/or gas production, materials may be subjected to high temperatures, high pressure and corrosive chemicals such as sour gas which is natural gas which includes significant amounts of hydrogen sulphide.
Often it is necessary to provide a seal between components which are part of an oil and gas installation. For example O-rings are often used in a valve where a seal is required between a valve shaft and valve housing. However, when O-rings are used in high pressure environments, the O-ring may have a tendency to extrude into the gap between the parts, resulting in failure of the seal. To address this problem, back-up rings are used in conjunction with O-rings, as illustrated in FIG. 1.
Referring to FIG. 1, there is shown a first circular cross-section part 2 within a second circular cross-section part 4. An elastomeric O-ring 6 is provided between the parts 2, 4 to seal the gap 8 therebetween. The parts 2, 4 are subjected to fluid pressure of for example up to 30,000 psi (207 Pa) (illustrated by arrows 10) and a temperature of about 500° F. and corrosive chemicals such as sour gas may be present. Under such conditions, there would be a tendency for seal 6 to extrude into gap 12 unless a back-up ring 14 was provided. Back-up ring 14 may comprise an endless single turn ring or may comprise a spiral. It is arranged to prevent extrusion of O-ring 6. Additionally, the back-up ring itself needs to resist extrusion into gap 12, when subject to the extreme conditions referred to.
It is very challenging to select a polymeric material which is able to withstand the harsh conditions encountered in oil and gas installations, for example subterranean installations. For example, polyetheretherketone (PEEK) is a high performance semi-crystalline polymer which is used in oil and gas applications. It has a very high chemical resistance; however, when used, for example, for a back-up ring, it extrudes significantly over time. Polyetherketone (PEK) is also used in the oil and gas industry. However, despite the fact it is highly crystalline, it is found to have poor chemical resistance to, for example sour gas, leading to its premature failure in use. Other semi-crystalline polymers such as polyetherketoneetherketoneketone (PEKEKK) also are found to show low corrosion resistance to sour gas and/or other fluids present in oil and gas environments.